scope:

Purpose

Design of modern application-specific integrated circuits, such as gate arrays or field programmable gate arrays (FPGAs), currently is achieved through a text-based approach-not via schematics. The text description is similar in appearance to a programming language such as C or Pascal. The purpose of this NASA Technical Handbook is to aid the design engineer in using good practices to produce quality designs, minimize errors, and produce a description that is maintainable and reviewable. This NASA Technical Handbook covers a hardware description language called very high-speed integrated circuit (VHSIC) hardware description language (VHDL).

VHDL is a large and powerful language. It is also extremely flexible, as there are many ways to describe a design or model. The variety of circuits, situations, and technologies the logic designer encounters are so varied that a one-size-fits-all solution is not practical and will needlessly constrain the design engineer or result in poor guidance. The intent of this NASA Technical Handbook is to cover most situations while giving the design engineer flexibility in the writing of the description. With the powerful VHDL language and very complex applicationspecific integrated circuits (ASICs) and FPGAs currently available, flexibility is needed in this design domain.

Because having no guidelines or rigidly enforcing rules in various domains hinders the goal of correct, maintainable, and reviewable descriptions, this NASA Technical Handbook takes a middle-ground approach, summarized by Brooks (1975) as follows:

At first sight, the idea of any rules or principles being superimposed on the creative mind seems more likely to hinder than to help, but this is quite untrue in practice. Disciplined thinking focuses inspiration rather than blinkers it.

Applicability

This NASA Technical Handbook is applicable to digital designs that are described by VHDL text. The principles that form the basis of this NASA Technical Handbook are applicable to other hardware description languages such as Verilog™.

This NASA Technical Handbook is approved for use by NASA Headquarters and NASA Centers, including Component Facilities and Technical and Service Support Centers. It may also apply to the Jet Propulsion Laboratory (a Federally Funded Research and Development Center), other contractors, recipients of grants, cooperative agreements, or other agreements only to the extent specified or referenced in the applicable contracts, grants, or agreements.

This NASA Technical Handbook, or portions thereof, may be referenced in contract, program, and other Agency documents for guidance.